[libmicrohttpd] Introducing a LMH version check in a configure.ac

[emmanuel]

Hi,

I use libmicrohttpd in my project and it works well, it does exactly what it 
has to do.

Unfortunately, my soft does not compile on "old" GNU/Linux distributions. I get 
this error:

file.cpp:279: erreur: invalid conversion from «int (*)(void*, MHD_Connection*, 
const char*, const char*, const char*, const char*, size_t*, void**)» to «int 
(*)(void*, MHD_Connection*, const char*, const char*, const char*, const char*, 
unsigned int*, void**)»

file.cpp:279: erreur:   initialising argument 5 of «MHD_Daemon* 
MHD_start_daemon(unsigned int, short unsigned int, int (*)(void*, const 
sockaddr*, socklen_t), void*, int (*)(void*, MHD_Connection*, const char*, 
const char*, const char*, const char*, unsigned int*, void**), void*, ...)»

It seems that the API was changed at the version 0.4.0 and in fact it works 
well with a recent version of LMH.
I want now to check that (the LMH version) in my configure.ac: I want to be 
certain that the system has a version of LMH at least higher than the 0.4.0.

How I can do that? I have seen MHD_VERSION in microhttpd.h but I do not 
understand how to make the relation between this hex. number and the human 
readable version numbers (like 0.4.0).

Regards
Emmmanuel